Google enables voice and video calls to other computers in 2008 and call phones in 2010 but until now you can only make call phones to one person from Gmail. Today Google announce on official Gmail blog that from now Google allow you to make or receive multiple calls in Gmail.
If you’re in a call with one person and want to make a second one, your first call will be put on hold while you talk on your new call. You can switch between calls by pressing the “Resume” button on the call you want to talk on, which will automatically put the previous call on hold.
Receiving incoming calls while you’re in another call is very easy now in Gmail, you’ll receive a notification of the incoming call and can choose to accept or reject. If you accept the new call and you already have one active call then the previous call will be put on hold. Also you can put any call on hold.
Multiple call feature works across all call types (voice, video, and phone). But this feature allow you to a maximum of two outgoing calls to physical phones can be placed at once.